Field of the Invention
The present invention provides a method for manufacturing a nitride phosphor, specifically through a hot isostatic pressing by using a barium-containing nitride as a flux.
Descriptions of the Related Art
White light-emitting diodes (WLED) have become the mainstream white light illumination system because it is small, stable and environmentally friendly and has good emission efficiency. All the experts in academia and industry are dedicating themselves to improving the emission performance of white light-emitting diodes to widen its application in human life.
The phosphor is one of the essential materials of light-emitting diodes. In 1996, a Japanese company, Nichia Chemical Company, invented a white light-emitting diode using a cerium-doped yttrium aluminum garnet (YAG) phosphor (Y3Al5O12:Ce3+, YAG:Ce). Such a phosphor can be excited to generate yellow light by using a blue light source (e.g., a blue light-emitting diode), and the generated yellow light can be mixed with the blue light from the blue light source to provide the desired white light. Such a white light-emitting diode is low-cost but poor on color rendering. Therefore, the technique of using a red phosphor in such a white light-emitting diode was then invented to improve color rendering.
Light-emitting diodes have replaced cold cathode fluorescent lamps that are used as the backlight of a back-lit display. Light-emitting diodes can not only effectively lower the power dissipation and heat loss of the display device, but also have a wider color gamut and are more environmentally friendly. The backlight is a common illumination form of display devices. The difference between backlight and front-light primarily lies in that the backlight allows light to be emitted from the side or back of the display device to increase the illumination in a low light condition or enhance the brightness of the computer display and liquid crystal monitor. In a back-lit liquid crystal display device, the light that radiates out from the light source is oriented through a polarizer to become unidirectional, so that photons are vibrated in a specific direction toward the liquid crystal molecular layer. The light, after passing through the polarizer, passes through the liquid crystal molecular layer, another polarizer and then a color filter, to show color images on the display panel. To achieve higher color purity, the display device may further comprise filters so that only a portion of the light emitted from the light-emitting diode with a specific wavelength can pass through the filters. However, such an arrangement will inevitably lower the performance of the display device. In view of this, the experts in the industry are focusing on the development of phosphors with narrow emission spectra.
Examples of phosphors include oxide phosphors and nitride phosphors. Nitride phosphors have therefore taken on increased significance in recent years because they have better thermal stability and more redshifted emission spectra by virtue of their firm structures and stronger electron cloud expansion effects. In terms of the red emission band, (Ca,Sr)AlSiN3:Eu2+ is one of the most notable nitride phosphors because it has an adjustable spectrum with a peak value ranging from about 620 nm to about 650 nm. However, this nitride phosphor has an overly broad emission spectrum, and a portion of the emission spectrum falls outside the sensitivity curve of the human eye so that the emission efficiency of the device will be lowered. In view of this, in 2014, Wolfgang Schnick et al. disclose a phosphor SrLiAl3N4:Eu2+ (SLA) with a narrow emission spectrum (referring to “Nature Materials, 2014, Vol. 13, p. 891-896”). The phosphor has a full width at half maximum (FWHM) of only 50 nm, an emission peak value of 650 nm, and good thermal stability. However, the phosphor must be synthesized through a radio frequency furnace by using hydrides or nitrides as starting materials under a mixed atmosphere of hydrogen and nitrogen. The complex synthesizing process makes the phosphor difficult to be mass-produced. Moreover, the emission efficiency of the synthesized phosphor is poor and needs to be improved.